1. Field of the Invention
This invention relates to the winding of a continuous web of material, such as paper manufactured on a papermaking machine. More particularly, this invention relates to the construction and control of a rider roll for applying pressure to a roll of paper being wound in a winder. Still more particularly, this invention relates to an articulated rider roll system comprising a multiple number of axially aligned individual wheel elements for applying a controlled nip force against the surface of a roll of paper being wound by controlling the movement of a beam on which the wheel elements are mounted, and against which they are biased, and the nip load force, both as a function of the paper roll diameter.
2. Description of the Prior Art
Rider rolls for stabilizing and controlling wound-in tension in the paper web in a winder have been used almost since the invention of the winder itself. The dynamics of winding an on-coming web of paper into a wound paper roll, which may be 30 feet long and 6 feet in diameter, requires careful support and pressure to maintain the wound-in web tension at desired levels at different radial distances in the diameter of the wound roll. Also important is the function of nip mechanics of the rider roll against the surface of the wound roll to provide the desired density of the wound roll while maintaining the desired web tension. Nip mechanics has been defined as a strain inducing mechanism that increases the sheet tension in the outside layers of a paper roll beyond the unwind stand tension.
The tension in the paper web at the rider roll nip controls the relative slippage between the first few layers of paper. After the paper web has been covered with several layers of on-coming paper, the wound-in tension at the surface has an effect on the paper previously wound, so it is important that the initial wound-in tension be controlled and correct for the diameter of the roll at each stage in its development.
Prior rider roll configurations have included a continuous metal roll extending across the entire working width of a winder, which essentially corresponds to the length of the paper roll being wound. As winder speeds increased, and as the length of the wound paper roll increased, improvements were made in the support provided by the rider roll by biasing the rider roll pneumatically against the wound paper roll (Printz et al, U.S. Pat. No. 3,237,877), and by forming the rider roll into segments extending axially across the width of the winder so that separate segments could have their ends separately biased to follow the contour of the paper roll being wound (Dorfel, U.S. Pat. No. 3,648,342 and Snygg et al, U.S. Pat. No. 4,095,755). Also known is the use of inflatable support drums and rider roll (Frye et al, U.S. Pat. No. 4,541,585) in a winder for the purpose of distributing the forces supporting the wound paper roll over a wider area to avoid crushing of the paper web and to distribute the wound-in web tension more evenly.
All of these apparatus provide some improvement in the support and distribution of the forces provided by the rider roll against the surface of the wound paper roll along its length. However, all of these prior systems have a common structural and operational deficiency in that the forces they provide by the rider roll against the wound paper roll vary in intensity across the machine width due to variations in paper profile in the cross-machine direction.
As a result of the variable nip force with which the rider roll in prior apparatus engages the surface of the wound paper roll, and considering that the localized diameter of the wound roll varies at different locations along the length of the roll due to variations in the caliper of the paper web, roll defects are caused or exacerbated by high localized nip loads where the diameter of the wound roll is slightly larger than the diameter of the roll at a location a short distance away along the longitudinal axis of the wound roll. Thus, local variations in the wound roll diameter, which themselves are undesirable, contribute to other defects, such as variations in the wound-in web tension by preventing continuous and uniform contact of other locations closely spaced along the length of the wound roll surface by the rider roll which is held away from the relatively lower surface areas of the wound paper roll by its contact over the relatively higher surface areas over the points of slightly greater localized diameters on the wound roll.